Model Diagnostic Discussion
NWS Weather Prediction Center College Park MD
113 AM EDT Fri Jul 19 2019

Valid Jul 19/0000 UTC thru Jul 22/1200 UTC

...See NOUS42 KWNO (ADMNFD) for the status of the upper air
ingest...

00Z Preliminary Model Evaluation Including Preference and Forecast
Confidence
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...Overall Pattern Across the CONUS...
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Preference: 00Z ECMWF/UKMET, 18Z GEFS mean
Confidence: Slightly below average

Through Saturday morning, a general model blend is acceptable as
most of the global suite is handling the large scale ridging
across the eastern 2/3 of the country similarly. Large
discrepancies creep up late on day 2 and especially into day 3
with respect to a shearing upper low across the CA/US border and
how this impacts the ridge breakdown into early next week.

The NAM continues to be quite strong and fast driving a trough
into the east, and knowing the typical model tendency to break
down these ridges too quickly suggests the NAM is likely too fast,
especially noting how strong the antecedent ridge is across the
east. The CMC starts in good agreement with the remaining suite,
but elongates the low dropping into the PacNW on day 3, which
causes downstream effects due to the amplification of the
mid-level pattern. Otherwise, the GFS/UKMET/ECMWF are in
reasonable agreement, but feature timing and intensity differences
of shortwave troughs/ridges moving through the fast northern tier
flow which have impact on the sensible weather related to any MCS
activity and the cold front moving into the eastern half of the
CONUS. The UKMET keeps the eastern ridge the strongest, which
seems plausible, while the ECMWF is consistent with its previous
runs, and closely aligned with the GEFS mean which is a bit slower
than the GFS Op. For this reason a blend of the GEFS/UKMET/ECMWF
is preferred, but some weight on the other models, especially
within 48 hours, is acceptable.


Model trends at www.wpc.noaa.gov/html/model2.html
500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml

Weiss